Primary Angioplasty for the Treatment of Acute ST-Segment Elevated Myocardial Infarction: An Evidence-Based Analysis

One of the longest running debates in cardiology is about the best reperfusion therapy for patients with evolving acute myocardial infarction (MI). Percutaneous transluminal coronary angioplasty (ANGIOPLASTY) is a surgical treatment to reopen a blocked coronary artery to restore blood flow. It is a type of percutaneous (through-the-skin) coronary intervention (PCI) also known as balloon angioplasty. When performed on patients with acute myocardial infarction, it is called primary angioplasty. Primary angioplasty is an alternative to thrombolysis, clot-dissolving drug therapy, for patients with acute MI associated with ST-segment elevation (STEMI), a change recorded with an electrocardiogram (ECG) during chest pain.This review of the clinical benefits and policy implications of primary angioplasty was requested by the Ontario Health Technology Advisory Committee and prompted by the recent publication of a randomized controlled trial (RCT) in the New England Journal of Medicine (1) that compared referred primary angioplasty with on-site thrombolysis. The Medical Advisory Secretariat reviewed the literature comparing primary angioplasty with thrombolysis and other therapies (pre-hospital thrombolysis and facilitated angioplasty, the latter approach consisting of thrombolysis followed by primary angioplasty irrespective of response to thrombolysis) for acute STEMI.There have been many RCTs and meta-analyses of these RCTs comparing primary angioplasty with thrombolysis and these were the subject of this analysis. Results showed a statistically significant reduction in mortality, reinfarction, and stroke for patients receiving primary angioplasty. Although the individual trials did not show significant improvements in mortality alone, they did show it for the outcomes of nonfatal reinfarction and stroke, and for an end point combining mortality, reinfarction, and stroke. However, researchers have raised concerns about these studies.A main concern with the large RCTs is that they lack consistency in methods. Furthermore, there is some question as to their generalizability to practice in Ontario. Across the RCTs, there were differences in the type of thrombolytic drug, the use of stenting versus balloon-only angioplasty, and the use of the newer antiplatelet glycoprotein IIb/IIIa. The largest trial did not offer routine follow-up angioplasty for patients receiving thrombolysis, which is the practice in Ontario, and the meta-analysis included trials with streptokinase, an agent seldom used in hospitals in Ontario. Thus, the true magnitude of mortality benefit can only be surmised from head-to-head comparisons of current standard therapies for primary angioplasty and for thrombolysis.By taking a more restrictive sample of the available studies, the Medical Advisory Secretariat conducted a review that was more consistent with patterns of practice in Ontario and selected trials that used accelerated alteplase as the thrombolytic agent.Results from this meta-analysis suggest that the rates for primary angioplasty are significantly better for mortality, reinfarction, and stroke, in the short term (30 days), and for mortality, reinfarction, and the combined end point at 6 months. When primary angioplasty was compared with in-hospital thrombolysis, results showed a significant reduction in adverse event rates associated with primary angioplasty. However, 1 large RCT of pre-hospital thrombolysis (i.e., thrombolysis given by paramedics before arriving at the hospital) compared with primary angioplasty documented that pre-hospital thrombolysis is an equivalent intervention to primary thrombolysis in terms of survival. Furthermore, a meta-analysis of studies that compared pre-hospital thrombolysis with in-hospital thrombolysis showed a reduction in all hospital mortality rates in favour of pre-hospital thrombolysis, supporting the findings of the pre-hospital thrombolysis study. (2)Clinical trials to date have reported that hospital stay is often reduced for patients who receive primary angioplasty compared with thrombolysis. Using a cost-analysis performed alongside the only study from Ontario, the Medical Advisory Secretariat concluded that there might be savings associated with primary angioplasty. These savings may partly offset the investment the provincial government would have to make to increase access to this technology. These savings should also be shown outside of a clinical trial protocol if the overall efficiencies of primary angioplasty are to be verified.Based on this health technology policy analysis, the Medical Advisory Secretariat concludes that primary angioplasty has advantages with respect to mortality and combined end points compared with in-hospital thrombolysis (Level 1 evidence). However, pre-hospital thrombolysis improves survival compared with in-hospital thrombolysis (Level 1 evidence) and is equivalent to primary angioplasty (Level 1 evidence).Results from the literature review raise concerns about the loss of therapeutic advantage due to treatment delays, time lapse from symptom onset to revascularization, time-of-day variations, the hospital volume of procedures, and the ability of hospitals to achieve in practice what RCTs have shown.Furthermore, questions relevant to applying primary angioplasty widely, involve the diagnosis by paramedics, ambulance diversion protocols, paramedic training, and inter-hospital transfer protocols. These logistical considerations need to be addressed to realise the potential to improve patient outcomes. In its analysis, the Medical Advisory Secretariat concludes that it is unrealistic to reorganise the emergency medical services across Ontario to fully implement a primary angioplasty program.Finally, it is important to evaluate the potential of this technology in the context of Ontario's health system. This includes urban and rural considerations, the ability to expand access to primary angioplasty and to minimize symptom-to-assessment time through a diverse strategy including public awareness. Therefore, a measured, evaluative approach to adopting this technology is warranted.Furthermore, the alternative approach to pre-hospital or early thrombolysis, especially within 120 minutes from onset of symptoms, should be considered when developing the approach to improving outcomes for acute MI. This could include efforts to decrease the symptom-to-thrombolysis time through strategies such as a concerted public education program to expedite presentation to emergency rooms after onset of symptoms, a pre-hospital ECG and thrombolysis checklist in ambulances to reduce door-to-needle time on arrival at emergency rooms, and, especially in remote areas, access to pre-hospital thrombolysis.The Medical Advisory Secretariat therefore recommends that this analysis of primary angioplasty be viewed in the overall context of all interventions for the management of acute MI and, in particular, of improving access to primary angioplasty and maximising the use of early thrombolysis.Outcomes for patients with acute MI can be improved if efforts are made to optimise the interval from symptom onset to thrombolysis or angioplasty. This will require concerted efforts, including public awareness through education to reduce the symptom-to-emergency room time, and maximising efficiencies in door-to-intervention times for primary angioplasty and for early thrombolysis.Primary angioplasty and early thrombolysis cannot be considered in isolation from one another. For example, patients who have persistent STEMI 90 minutes after receiving thrombolysis should be considered for angioplasty ("rescue angioplasty"). Furthermore, for patients with acute MI who are in cardiac shock, primary angioplasty is considered the preferred intervention. The concomitant use of primary angioplasty and thrombolysis ("facilitated angioplasty") is considered experimental and has no place in routine management of acute MI at this time. In remote parts of the province, consideration should be given to introducing pre-hospital thrombolysis as the preferred intervention through upgrading a select number of paramedics to advanced care status.